A known method for producing optoelectronic components, in particular for producing light emitting diodes on the basis of nitride compound semiconductors, is based on so-called thin-film technology. In this method, a functional semiconductor layer sequence, which in particular comprises a radiation-emitting active layer, is firstly grown epitaxially on a growth substrate, then a new carrier is applied to the surface of the semiconductor layer sequence opposite to the growth substrate, and the growth substrate is subsequently separated off. The growth substrates used for nitride compound semiconductors, are relatively expensive. Examples of such growth substrates are SiC, sapphire and GaN. Because the growth substrates are comparatively expensive, this method affords the advantage, in particular, that the growth substrate is reusable. A growth substrate made of sapphire can be stripped away from a semiconductor layer sequence made of a nitride compound semiconductor for example by means of a laser lift-off method known from WO 98/14986.
A thin-film LED is distinguished in particular by the following characteristic features:                a reflective layer (mirror layer) which reflects at least part of the electromagnetic radiation generated in the epitaxial layer sequence back into the latter is applied or formed at a main area of a radiation-generating epitaxial layer sequence that faces a carrier;        the epitaxial layer sequence has a thickness in the region of 20 μm or less, in particular in the region of approximately 6 μm; and        the epitaxial layer sequence contains at least one semiconductor layer with at least one area which has an intermixing structure which ideally leads to an approximately ergodic distribution of the light in the epitaxial layer sequence, that is to say that it has an as far as possible ergodically stochastic scattering behavior.        
A basic principle of a thin-film LED is described for example in I. Schnitzer et al., Appl. Phys. Lett. 63 (16), Oct. 18, 1993, 2174-2176, the disclosure content of which is hereby incorporated by reference.
Electrical contact is made with thin-film LEDs generally by means of two electrical contact layers, for example by means of a p-type contact layer on the rear side of the carrier and an n-type contact layer on the side of the semiconductor layer sequence that is remote from the carrier. In general, the side of the thin-film LED that is remote from the carrier is provided for coupling out radiation, so that a contact layer that is non-transparent to the emitted radiation can only be applied to a partial region of the surface of the semiconductor layer sequence. For this reason, often only a comparatively small central region of the chip surface is provided with a contact area (bonding pad).
In conventional light-emitting diode chips having an edge length of less than 300 μm, in general a comparatively homogeneous current distribution in the semiconductor chip can already be achieved by means of a bonding pad arranged centrally on the chip surface.
In the case of large-area semiconductor chips having an edge length of approximately 1 mm, by way of example, this type of contact-making may, however, disadvantageously lead to an inhomogeneous current feed into the semiconductor chip, which leads to an increased forward voltage and to a lower quantum efficiency in the active zone. This effect occurs in particular in the case of semiconductor materials which have a low transverse conductivity, in particular in the case of nitride compound semiconductors. The maximum current density occurs in a central region of the semiconductor chip in this case. However, the radiation emitted in said central region of the semiconductor chip is at least partly emitted toward the non-transparent bonding pad and thus at least partly absorbed.
In order to improve the current expansion, it is known for example to apply a thin semitransparent metalization layer, for example Pt or NiAu, over the whole area of the chip surface of a p-type semiconductor material. In this case, however, a non-negligible part of the emitted radiation, for example approximately 50%, is absorbed in the semitransparent layer. Furthermore, such contact layers are not readily suitable for making contact with n-doped nitride compound semiconductors.
In order to improve the coupling-in of current in the case of InGaAlP LEDs, it is known from DE 199 47 030 A1 (which corresponds to U.S. patent application Ser. No. 10/089,017) to use a relatively thick, transparent current expansion layer provided with a laterally patterned electrical contact layer. In this case, the current is impressed through a central bonding pad and also through a plurality of contact webs connected to the bonding pad on the chip surface. This type of contact-making cannot readily be applied to large-area light-emitting diode chips which contain a semiconductor material having a low transverse conductivity, in particular nitride compound semiconductors, since the density of the non-transparent contact webs on the chip surface would have to be increased in such a way that a large part of the emitted radiation would be absorbed in the contact layer. A comparatively thick current expansion layer furthermore leads to an increased voltage drop and takes up a long growth time during production. Furthermore, strains may occur in a comparatively thick current expansion layer and cracks may possibly be induced by said strains.